DRAWING

Check if a world is a BWorld or a GWorld

A GWorld pointer is a valid grafport pointer. Look into the pointer as though it were a grafport. Get the rowbytes field. If rowbytes% AND &C000 is anything other than zero, you have a more-than-one-bit-deep grafport.

Since your application always creates a GWorld for >1 bit uses, you know that any colour grafport is also a GWorld.